1. Field of the Invention
This invention pertains generally to inline optical sensors for obtaining data from a fluid product stream and, more particularly, to apparatus for cleaning optical windows in such sensors.
2. Related art
Inline measurement sensors such as spectrophotometers, colorimeters, turbidimeters, refractometers, ultrasonic flow and particle sensing devices, and the like, have optical windows through which measurements are made on fluid product streams. To have reliable measurements, it is important that the window surfaces remain clean and free of films, dirt or other contamination. Unfortunately, since the windows are in contact with the product streams, they are susceptible to contamination and fouling thereby. This contamination can introduce errors into a measurement or even prevent the measurement from being made.
Measurements such as low turbidity are particularly susceptible to fouling of window surfaces by the product stream. This fouling results in the scattering of the light beam and is seen by the detector as suspended solids in the product stream. In low level measurements, e.g. 5.0 ppm or less, the scattering due to window fouling can exceed the scattering produced by the suspended solids. Examples of low level turbidity measurements where potential window fouling is high include measurements of oil in water, suspended solids in potable water and waste treatment effluents.
Heretofore, there have been attempts to clean the windows of inline optical sensors by techniques such as purging with water and/or another liquid, ultrasonic cleaning, and the application of protective coverings. None of the techniques, however, has provided a consistent and controllable cleaning of the critical optical surfaces.
It is in general an object of the invention to provide a new and improved apparatus for cleaning windows of inline optical sensors which come into contact with product streams.
Another object of the invention is to provide a window cleaner of the above character which overcomes the limitations and disadvantages of the techniques heretofore employed for cleaning the windows of inline sensors.